Aluminoxane compositions are widely used in combination with various types of metallocenes and transition metal compounds to prepare catalyst systems for polymerizing olefin monomers. However, certain limitations are associated with standard aluminoxane solutions, such as poor solubility, instability, and gel formation. For example, solutions of conventional aluminoxanes, such as methylaluminoxane (MAO), must be kept at lower temperatures to inhibit degradation via irreversible gel formation.
Addition of small amounts of halogen to conventional aluminoxanes has been shown to impart a higher stability to precipitation, i.e., gel formation, at ambient and elevated temperatures. See, for example, US 2005 0143254 (publication of Ser. No. 10/751,144 filed 31 Dec. 2004). Gel formation is undesirable because if causes the aluminoxane to be difficult to handle. For example, whereas liquid aluminoxanes can be readily transferred from container to reactor via tubing, transfer of a gel from container to reactor can be challenging and time consuming.
While aluminoxanes with halogen added are generally more stable to precipitation than standard aluminoxanes, they are still nonetheless susceptible to some precipitation at room temperature (about 20° C.) and higher temperatures.
It is therefore desirable to provide aluminoxane compositions that have greater solubility at lower temperatures and are resistant to irreversible precipitation at higher temperatures.